REST API "Failed to create service account from Hub, giving up" error

Hi! I'm trying to receive data from REST Api after Authorization in Hub. Here is my actions:

1. Authenticate application in Hub using Client credentials flow (by the way, is it right flow choice for chat bot?)

POST /api/rest/oauth2/token HTTP/1.1
Host: hub.example.com
Authorization: Basic BLA_BLA
Content-Type: application/x-www-form-urlencoded

grant_type=client_credentials&scope=YOUTRACK_ID

2. Then i'm trying to get issues from YouTrack, using recieved access token

GET /rest/issue HTTP/1.1
Host: yt.example.com
Authorization: Bearer ACCESS_TOKEN
Accept: application/json

Response has status 500 with this message
{"value": "Failed to create service account from Hub, giving up"}

What's going on and what should i do? Thanks